U.S. patent number 3,921,445 [Application Number 05/406,553] was granted by the patent office on 1975-11-25 for force and torque sensing method and means for manipulators and the like.
This patent grant is currently assigned to Stanford Research Institute. Invention is credited to John W. Hill, Antony J. Sword.
United States Patent |
3,921,445 |
Hill , et al. |
November 25, 1975 |
Force and torque sensing method and means for manipulators and the
like
Abstract
A manipulator is shown of the type which includes an effector,
such as a hand, comprising a pair of jaws relatively pivotally
movable between open and closed positions under operation of power
means such as an electric motor. Sensing means, for sensing both
magnitude and direction of forces along three mutually orthogonal
axes intersecting at the wrist and for sensing magnitude and
direction of torques about said axes, are provided at the wrist
intermediate to the manipulator hand and hand supporting means. The
sensing means includes a plurality of sensing units radially spaced
from the longitudinal axis of the manipulator at equal distances
therefrom. In an exemplary arrangement, four such orthogonally
located sensing units are employed, each of which includes a
radially extending opaque pin carried by the manipulator arm or
hand. Each pin extends into a clearance hole formed in an energy
source and detector housing carried by the other of the arm and
hand. The housings also are formed with passages which intersect
the pin receiving hole and along which passages an associated
energy source and energy detector are located, with the energy from
the source being directed toward the energy detector. A portion of
the energy from each of the sources is blocked by the pin such that
only the unobstructed portion of the energy from the source reaches
the detector. The amount of shadowing of energy by the pins depends
upon forces and torques applied to the hand, and the outputs from
the detectors are combined in such a manner as to provide output
signals representative of the three components of force at the
wrist corresponding to reach, lift and sweep directions of hand
motion and the three components of torque corresponding to twist,
turn and tilt of the hand. Also, the hand and power means for
operation of the hand are located at opposite sides of the wrist,
such that the power means functions as a counterweight to balance
the weight of the hand. Consequently, the hand weight is not
reflected in the outputs of the torque sensors.
Inventors: |
Hill; John W. (Palo Alto,
CA), Sword; Antony J. (San Francisco, CA) |
Assignee: |
Stanford Research Institute
(Menlo Park, CA)
|
Family
ID: |
23608477 |
Appl.
No.: |
05/406,553 |
Filed: |
October 15, 1973 |
Current U.S.
Class: |
73/862.043;
901/32; 414/5; 901/38 |
Current CPC
Class: |
G01L
1/24 (20130101); G01L 5/166 (20130101); G01L
5/226 (20130101); G01L 5/163 (20130101); B25J
19/021 (20130101) |
Current International
Class: |
B25J
19/02 (20060101); G01L 5/22 (20060101); G01L
1/24 (20060101); G01L 5/16 (20060101); G01l
005/16 () |
Field of
Search: |
;73/133R ;250/231R,231P
;244/83E ;214/1CM |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Ruehl; Charles A.
Attorney, Agent or Firm: Beckman; Victor R.
Government Interests
The invention described herein was made in the course of work under
a grant or award from the United States National Science
Foundation.
Claims
We claim:
1. Sensing means for use in sensing at least one component of force
and torque components along mutually orthogonal X, Y and Z axes
transmitted between first and second members having a longitudinal
axis extending along the Z axis, said sensing means comprising:
resilient coupling means coupling said first and second members to
allow for relative movement therebetween and through which said X,
Y and Z axes extend;
a plurality of sensing units radially displaced from said Z axis at
the resilient coupling means, each of which sensing units includes
first and second cooperating means attached to said coupled first
and second members, respectively, so that relative movement between
said first and second cooperating means is produced upon
transmission of forces and torques between said coupled first and
second members through said resilient coupling means; said forces
and torques being transmitted through said resilient coupling means
substantially independently of said sensing units, and
means for obtaining at least first and second electrical outputs
from each of said sensing units, the outputs from each sensing unit
being respectively responsive only to relative movement of said
cooperating means along a first direction perpendicular to the
radius extending from the Z axis through the associated sensing
unit and responsive only to relative movement of said cooperating
means along a direction mutually orthogonal to said associated
first direction and radius.
2. The sensing means as defined in claim 1 wherein said sensing
units are of the non-piezoelectric type.
3. The sensing means as defined in claim 1 wherein:
said plurality of said sensing units are circumferentially spaced
about said longitudinal axis at the resilient coupling means; and
including
means for connecting electrical outputs from different sensing
units together in circuit arrangements having outputs algebraically
related to said electrical outputs from said sensing units.
4. The sensing means as defined in claim 1 wherein said first and
second cooperating means of each said sensing unit include an
opaque member and spaced apart light source and photocell,
respectively, arranged so that light from the source is directed
toward said photocell past an edge of said opaque member, which
opaque member blocks a variable portion of the light preventing the
same from reaching the photocell.
5. The sensing means as defined in claim 1 wherein said first and
second cooperating means of each of said sensing units include a
potentiometer comprising a resistive element with parallel
extending terminals along opposite edges thereof and a contact in
movable engagement with the resistive element, respectively.
6. The sensing means as defined in claim 1 wherein said first and
second cooperating means of each said sensing unit include a pair
of adjacent photocell elements and a light source, respectively,
arranged so that light from the source is directed radially onto
both of said photocell elements.
7. The sensing means as defined in claim 1 which includes:
first and second of said sensing units diametrically oppositely
located along said Y axis; said first and second electrical outputs
from each of said sensing units being responsive only to relative
movement of said cooperating means along directions parallel to
said X and Z axes, respectively.
8. The sensing means as defined in claim 7 including:
means for connecting electrical outputs from said first and second
sensing units together in circuit arrangements having outputs
algebraically related thereto, one of said circuit arrangements
having an output indicative of force transmitted along said X axis,
and another of said circuit arrangements having an output
indicative of torque about the X axis.
9. The sensing means as defined in claim 8 wherein another of said
circuit arrangements has an output indicative of torque about the Z
axis.
10. The sensing means as defined in claim 8 wherein another of said
circuit arrangements has an output indicative of force transmitted
along said Z axis.
11. The sensing means as defined in claim 8 including:
a second pair of said sensing units diametrically oppositely
located along said X axis, said first and second electrical outputs
from each sensing unit of said second pair thereof being responsive
only to relative movement of said cooperating means along
directions parallel to said Y and Z axes, respectively;
means for connecting the electrical outputs from said second pair
of sensing units together in circuit arrangements having outputs
indicative of force transmitted along and transmitted torque about
said Y axis.
12. Sensing means for use in sensing at least one component of
force and torque components along mutually orthogonal X, Y and Z
axes transmitted between first and second members having a
longitudinal axis extending along the Z axis, said sensing means
comprising:
resilient coupling means coupling said first and second members to
allow for relative movement therebetween and through which said X,
Y and Z axes extend;
at least one sensing unit radially displaced along the Y axis from
said Z axis at the resilient coupling means, which sensing unit
includes first and second cooperating means attached to said
coupled first and second members, respectively, so that relative
movement between said first and second cooperating means is
produced upon transmission of forces and torques between said
coupled first and second members through said resilient coupling
means; and
means for obtaining a first electrical output from said sensing
unit responsive only to relative movement of said cooperating means
along a first direction parallel to said longitudinal axis; said
first and second members comprising a manipulator and effector and
end effector supporting means, respectively, interconnected by said
resilient coupling means.
13. The sensing means as defined in claim 12 wherein said end
effector comprises:
a pair of relatively movable members;
a motor for operating said movable members; and
means for mounting said motor along said Z axis at the side
opposite sais sensing unit from the manipulator end effector to
counterbalance said end effector.
14. Sensing means for use in sensing components of force and torque
along mutually orthogonal X, Y and Z axes extending through
resilient coupling means coupling first and second members
together, said Z axis extending longitudinally therethrough;
at least three sensing units circumferentially spaced about said Z
axis about said resilient coupling means;
each of said sensing units including first and second cooperating
means attached to said coupled first and second members,
respectively, so that relative movement between said first and
second cooperating means is produced upon transmission of forces
and torques through said resilient coupling means;
means for obtaining first electrical outputs from each of said
sensing units responsive only to relative movement of said
cooperating means along a direction parallel to said Z axis;
first circuit means;
means for combining said first electrical outputs in said first
circuit means for obtaining outputs indicative of torque components
about said X and Y axes and the force component along said Z
axis;
means for obtaining second electrical output from each of said
sensing units responsive only to relative movement of said
cooperating means along a direction mutually orthogonal to the
radius through said sensing unit and the direction parallel to said
Z axis;
second circuit means; and
means for combining said second electrical outputs in said second
circuit means for obtaining outputs indicative of the force
components along said X and Y axes and the torque component about
said Z axis.
15. The sensing means as defined in claim 14 wherein there are four
of said sensing units circumferentially spaced about the Z axis
along said X and Y axes.
16. The sensing means as defined in claim 14 wherein said first and
second cooperating means include an opaque member and spaced apart
light source and photocell, respectively, arranged so that light
from the source is directed toward said photocell past an edge of
said opaque member, which opaque member blocks a variable portion
of the light preventing the same from reaching the photocell.
17. The sensing means as defined in claim 14 wherein said first and
second cooperating means of each sensing unit include a
potentiometer comprising a resistive element with parallel
extending terminals along opposite edges thereof and a contact in
movable engagement with the resistive element, respectively.
18. The sensing means as defined in claim 14 wherein said first and
second cooperating means include a pair of adjacent photocell
elements and a light source, respectively, arranged so that light
from the source is directed radially onto both of said photocell
elements.
19. The sensing means as defined in claim 14 wherein said first and
second members comprise a manipulator end effector and end effector
supporting means, respectively, interconnected by said resilient
coupling means.
20. The sensing means as defined in claim 19 wherein said end
effector comprises:
a pair of relatively movable members;
a motor for operating said movable members; and
means for mounting said motor along said Z axis at the side
opposite said sensing unit from the manipulator end effector to
counterbalance said end effector.
21. A method of sensing components of torque and force transmitted
between first and second members along mutually orthogonal X, Y and
Z axes comprising:
attaching said first and second members together by resilient
coupling means through which substantially the entire force and
torque components are transmitted between said first and second
members;
attaching a plurality of two-part sensing units, at
circumferentially spaced locations about the Z axis in the plane of
the X and Y axes, to said first and second members such that
relative movement between the two parts of the sensing units is
produced upon transmission of forces and torques through said
resilient coupling means;
obtaining first electrical outputs from the sensing units in
response to relative movement of the two parts along a direction
parallel to the Z axis;
combining the first electrical outputs in different combination to
obtain outputs related to torque components about said X and Y axes
and the force component transmitted along said Z axis;
obtaining second electrical outputs from the sensing units in
response to relative movement of the two parts of each sensing unit
along a direction mutually orthogonal to the associated radius
through said sensing unit and the direction parallel to the Z axis;
and
combining the second electrical outputs from the sensing units in
different combinations to obtain outputs related to force
components transmitted along said X and Y axes and the torque
component about said Z axis.
22. Sensing means for use in sensing at least one component of
force and torque components transmitted between first and second
members having a longitudinal axis extending therebetween
comprising:
resilient coupling means coupling said first and second members to
allow for relative movement therebetween;
an opaque member located along a radius extending from said
longitudinal axis;
housing means having a clearance hole into which said opaque member
extends;
means for attaching said opaque member and housing means to said
first and second members so that relative movement is produced
therebetween upon transmission of force and force moments through
said resilient coupling means;
means forming at least one light passage in said housing means
which intersects with said clearance hole formed therein; and
light source and light sensing means at said light passage with
said light sensing means arranged to receive light emitted by said
light source after passing an edge of said opaque member which
blocks a variable portion of the light depending upon force and
force moments transmitted by said resilient coupling means.
23. The sensing means as defined in claim 22 including;
a plurality of said light passages formed in said housing means
which intersect with said clearance hole and extending along
generally perpendicular axes, and
light source and light sensing means at opposite ends of each of
said light passages.
Description
BACKGROUND OF INVENTION
Position controlled manipulators for industrial and scientific use
are well known and often are used in automatic operations of
manufacture, assembly, etc. Control systems for the automatic
control and/or operation of manipulators may be of the open loop or
closed loop type. Closed loop systems generally necessitate the use
of a computer, such as a digital computer, to handle the necessary
coordinate conversions, control equations and completion criteria.
To carry out an assigned manipulative task requires the sensing of
torques and forces at various manipulator locations. Forces or
torques at the joints of the manipulator may be sensed by measuring
the current supplied to driving motors of the back pressure in
hydraulic systems used to operate the joints. Such joint force
measurements are of limited usefulness, however, for a number of
reasons including contamination by both the weight of the
manipulator segments and the weight of the load and the presence of
friction in the back drivability of individual joints. For example,
depending on the gearing employed, more than 10 percent of the
force exerted by a joint may be required to back drive the same.
The use of joint forces, therefore, is best suited to the detection
of collisions of the manipulator with obstacles encountered during
a task.
Another means of measuring contact between the manipulator end
effector (such as manipulator hand) and the environment is to
measure the force couple at some point on the manipulator,
preferably as close to the end effector as possible. The force
couple consists of a torque vector and a force vector describing
the reaction at said point. By sensing of the force couple at the
wrist, gravitational and acceleration loading on the manipulator
components behind the wrist have no effect on the sensing
mechanism, and only gravity and acceleration loading from the
combined mass of the end effector (e.g., hand) and object gripped
determine the force couple at the wrist. A computer controlled arm
employing wrist sensing means is shown, for example, in the article
entitled "Force Feedback of a Teleoperator System" by R. C. Groome,
Jr., MIT Charles Stark Draper Lab. Report T-575, Cambridge, Mass.,
August 1972. The present invention is directed to a greatly
simplified wrist sensor adapted for operation over a wide load
range.
SUMMARY OF INVENTION
An object of this invention is the provision of improved sensing
method and means for sensing torque and force vector quantities,
which sensing method and means are particularly adapted for use as
a wrist sensor of a manipulator.
An object of this invention is the provision of a simplified method
and means for sensing torques about three orthogonal axes and
forces along said axes, in which each torque and force measurement
is substantially independent of every other measurement.
An object of this invention is the provision of a manipulator which
is provided with force and torque sensing means in which said
torque and force sensing means are substantially unresponsive to
the weight of the manipulator hand.
The above and other objects and advantages are achieved by use of a
plurality of sensing units positioned a radially spaced distance
from the longitudinal axis of a resilient coupling means connecting
supported and supporting members such as a manipulator hand and
hand supporting means. The sensing units each have relatively
movable sections attached to the resilient coupling means so that
movement therebetween is produced upon transmission of forces and
force movements through the coupling means. Signals are produced by
the sensing units, which signals are related to components of
relative movement of the sensor sections in two orthogonal
directions mutually orthogonal to the direction of the radius to
the sensing unit. The sensing units are insensitive to relative
radial movement of the sensing sections. Signals from sensing units
are combined to obtain outputs indicative of at least one component
of the force and torque components present at the coupling means.
The sensing units may include potentiometers, photocells, split
photocells, or the like. In accordance with another feature of this
invention, the drive motor for actuation of the end effector is
fixedly secured thereto and is located at the opposite side of the
resilient coupling from the end effector to counterbalance the
same. Consequently, torque signals provided by the sensing
arrangement are uncontaminated by the weight of the hand.
BRIEF DESCRIPTION OF DRAWINGS
In the drawings, wherein like reference characters refer to the
same parts in the several views:
FIG. 1 is a plan view of a novel manipulator embodying this
invention, showing portions of the wrist sensor and jaw actuating
mechanism broken away for clarity;
FIG. 2 is a view taken substantially along line 2--2 of FIG. 1;
FIG. 3 is a fragmentary exploded view of the manipulator and
including an identification of the wrist axes and the forces along
and torques about which axes the wrist sensing means are
responsive;
FIG. 4 is a sectional view taken along line 4--4 of FIG. 1;
FIG. 5 is a sectional view taken substantially along line 5--5 of
FIG. 4 showing one of the sensing units;
FIG. 6 is an enlarged perspective view of one of the sensor unit
housings;
FIG. 7 is a schematic circuit diagram showing a pair of photocells
connected together in a difference circuit arrangement;
FIG. 8 is a longitudinal sectional view of a coupling means showing
a modified form of sensing units employing potentiometers;
FIG. 9 is a sectional view taken along line 9--9 of FIG. 8 showing
the resistance elements of the potentiometers;
FIG. 10 is a circuit diagram showing outputs from a pair of
potentiometers supplied to two difference circuits having outputs
indicative of force and torque at different axes;
FIG. 11 is a longitudinal sectional view of a coupling means
showing a further modified form of sensing units employing split
photocell elements; and
FIG. 12 is a sectional view taken along line 12--12 of FIG. 11
showing the photocell faces.
DESCRIPTION OF PREFERRED EMBODIMENTS
Reference now is made to FIGS. 1, 2 and 3 of the drawings wherein
the manipulator is shown comprising a hand supporting member 10
adapted to be coupled by threads 12 to a robot, automated
machinery, earth, space or underwater vehicle, or the like (not
shown) such as are presently in use. The member 10 is coupled
through the novel wrist sensing means of this invention, identified
generally by the reference numeral 14, to a gear box or housing 16
included in the manipulator hand. A detailed description of the
wrist sensing means is contained hereinbelow.
For present purposes, it will be understood that the wrist sensor
includes a ring 18, one side of which is secured to the base 22 of
the housing 16 as by screws 24 extending through holes in the base
into threaded holes in the ring to secure the base and ring
together. A reversible motor 20 is secured to this assemblage by
means of screws 23 extending through threaded holes in a flange 22'
on the base 22 of the housing 16 into holes in the motor base.
Resilient coupling means 26, such as pads of rubber or like
resilient material, are cemented or otherwise suitably secured
between the forward face 27 of the member 10 and rearward face 28
of the ring 18 to secure the ring 18 (with the attached gear
housing 16 and motor 20) to the member 10. The resilient coupling
means 26 are deformed upon transmission of forces therethrough, and
orthogonally positioned sensing units 25-1, 25-2, 25-3 and 25-4
located adjacent the coupling means provide a measure of the force
and torque at the intersection of the X, Y and Z axes identified in
FIG. 3.
The reversible motor 20 serves to open and close a pair of jaws 29
and 30 through a suitable gear and linkage mechanism which now will
be described. The motor shaft 32 extends through the ring 18 and an
aperture in the base plate 22 and into the housing 16. A pinion 34
at the forward end of the motor shaft engages a pair of inwardly
facing bevel gears 36 and 38 which are independently rotatably
supported on a shaft 40 extending between the upper and lower walls
42 and 44, respectively, of the housing 16, as seen in FIG. 2. The
upper wall 42, which is removable to facilitate assembly, is shown
broken away for clarity in FIG. 1. Attached to or fromed on the
bevel gears 36 and 38 at the outer sides thereof are spur gears 46
and 48 which engage sector gears 50 and 52, respectively, for drive
actuation thereof. The sector gears 50 and 52 are rotatably mounted
on shafts 54 and 56, respectively, extending between the upper and
lower walls of the housing 16.
A first pair of parallel links 58 and 60 connect the one jaw 29 to
the gear housing 16, and a similar second pair of parallel links 62
and 64 connect the other jaw 30 to the housing. At the housing the
links 58 and 62 are pivotally supported on the shafts 54 and 56
about which the sector gears pivot. The links 60 and 64 are
pivotally mounted on shafts 66 and 68 between the housing walls 42
and 44. Pins 70 connect the forward ends of the links 58, 60, 62
and 64 to the jaws 29 and 30. The inner links 58 and 62 are slotted
to receive the sector gears 50 and 52, respectively, and screws 72
secure the links to the gears.
Operation of the jaws 29 and 30 between open and closed position,
although believed to be apparent, will now be briefly described.
When the motor 20 is energized for rotation of the bevel gear 34,
the meshing bevel gears 36 and 38 are counterrotated. The
counterrotating gears 36 and 38 drive the gear segments 50 and 52
in counterrotating directions through the spur gears 46 and 48. The
links 58 and 62 attached to the gear segments are thereby
counterpivoted for closing or opening of the jaws. The links 60 and
64, which are parallel to the driven links 58 and 62, respectively,
maintain the jaw faces in parallel relation.
The jaws 29 and 30 may be of a generally hollow construction to
accommodate force sensors having actuating means at the jaw faces.
As seen in FIGS. 1 and 2, the inner facing walls of the jaws may be
provided with 18 force transducers actuated by a 3.times.6 array of
actuating members such as buttons 76. Other force transducers are
included which are under control of actuating plates 78-1 through
78-7 at other jaw surfaces. Also, mounted within the jaws and
extending from the inner jaw faces are slip sensors 80 which are
orthogonally positioned for sensing object slip transversely and
longitudinally of the jaw faces. The force and slip sensors are
disclosed and claimed in a copending patent application being filed
concurrently herewith and entitled "Manipulator with
Electromechanical Transducer Means", which application is assigned
to the assignee of the present application by the inventors, John
W. Hill and Antony J. Sword. The subject matter of the copending
application is specifically incorporated herein by reference.
The novel wrist sensing means of this invention includes, as
mentioned above, the four sensing units 25-1, 25-2, 25-3 and 25-4
located along the X-Y axes thereof. The Z axis of the three
mutually orthogonal axes extends along the longitudinal center of
the manipulator. The sensing means functions to sense the direction
and magnitude of forces acting along the three axes and the
direction and magnitude of the force moments thereabout. Where the
sensing means are employed in a manipulator, as shown in FIGS. 1-7
of the drawings, the forces along the X, Y and Z axes comprise
sweep, lift and reach forces, respectively, and the force moments
thereabout comprise tilt, turn and twist torques, respectively. In
FIG. 3, arrows indicating positive direction of torque about the X,
Y and Z axes are identified as M.sub.x, M.sub.y and M.sub.z,
respectively.
As best seen in FIGS. 1, 3 and 4, the member 10 comprises a
cylindrically shaped housing having at the forward end thereof
forwardly extending quadrature spaced arm members 82. Threaded
holes are formed through the arms 82 for the support of radially
extending opaque pins 84 having enlarged threaded heads in threaded
engagement with the threaded holes. The pins, as will become
apparent hereinbelow, function to block varying amounts of light
along light paths extending generally tangentially to the pins,
with the amount of light passing thereby being dependent upon the
forces and torques at the sensor. The ring 18 similarly is provided
with rearwardly extending quadrature spaced arm members 86 radially
spaced from the arms 82. In the illustrated arrangement, the arms
86 are inwardly radially spaced from the arms 82 and support
housing members 88, which are attached thereto by screw fasteners
90 extending through symmetrically located holes in the arms and
engaging threaded holes 92 (see FIG. 6) in the housing members. The
arms 86 and attached housings 88 are formed with colinear clearance
holes 94 and 96, respectively, into which the opaque pins 84
axially extend. The pins are spaced from the hole walls to allow
for displacement of the normally coaxially extending pin and hole
axes in operation.
For simplicity of manufacture all of the housing members 88 may be
of identical construction comprising, in addition to the mounting
holes 92 and pin receiving hole 96, light passages 98 extending
therethrough. The light passages 98 intersect the pin receiving
aperture 96, with the axes thereof extending substantially
tangentially of the pin 84 when the pin and aperture 96 are
coaxially located. In the illustrated arrangement there are four
parallel extending light passages which terminate at one pair of
opposite faces of the generally cubical housing 88 and two parallel
extending light passages which terminate in another pair of
opposite housing faces, with none of the light passages
intersecting any other light passage. In attaching the housings 88
to the arms 86, one housing 88 (at sensing unit 25-1) is arranged
with the four light passages 98 extending parallel with the
longitudinal Z axis, and the other three housings 88 (at sensing
units 25-2, 25-3 and 25-4) are arranged with the two parallel light
passages extending parallel with the Z axis.
Not all of the light passages are utilized in the sensing operation
but, as mentioned above, are formed in the housings 88 for
uniformity and simplicity of construction. Certain passageways are
provided with light source and light sensing means identified
generally by reference numerals 100 and 102, respectively, at
opposite ends of the passageways. The light source and sensing
means may comprise, for example, light emitting diodes and
phototransistors, respectively, although it will be apparent that
the invention is not limited to the use of such means. To
differentiate between the various light source and sensing means in
the description and drawings, the reference numerals 100 and 102
are followed by abbreviations for identification of the force or
torque sensed thereby together with a plus or minus sign for
indicating direction thereof. For example, reference characters
102X.sup.+ and 102X.sup.- identify the two sensing means used in
the measurement of forces along the X axis. Similarly the reference
characters 102M.sub.x and 102M.sub.x identify those sensing means
used in the measurement of the moments of force (i.e., torque)
about the X axis. The light source and sensing means employed in
the force and torque measurements about the Y and Z axes are
similarly identified.
As noted above, the axes of the light passages extend substantially
tangentially of the opaque pins 84 in the neutral, central position
of the pins within the clearance holes 96. In this position, as
seen in FIGS. 4 and 5, the pins shield approximately half the light
from each source 100, preventing the shielded portion from reaching
the associated photocell at the opposite end of the passageway.
That is, the shadow of the pin covers approximately one half the
active face of the associated photocell, with the pin centrally
axially located in the clearance hole. Movement of the opaque pin
within the clearance hole toward or away from the light beam
increases of decreases the shielding effect by the pin to decrease
and increase, respectively, the amount of light reaching the
associated photocell. Where the photocells comprise
phototransistors, the output therefrom increases with an increase
in light received.
It will here be noted that any change in the amount of light from a
light source passing a pin 84 is dependent upon that component of
relative movement of the pin axis toward or away from the light
beam axis and is substantially independent of movement in any other
direction. Referring to FIG. 5, for example, it will be apparent
that movement of the pin 84 to the left along the X axis will block
more light from the source 100M.sub.z .sup.+, thereby casting a
larger shadow in the photocell 102M.sub.z .sup.+ to decrease the
photocell output. Movement of the pin along the Z axis merely moves
the pin along the light beam axis between the source 100M.sub.z
.sup.+ and sensor 102M.sub.z .sup.+ without producing a significant
change in the amount of light passing the pin. Similarly, movement
of the pin along the Y axis, into or out of the plane of the
drawing figure, has no effect on the light passage between said
source 100M.sub.z .sup.+ and sensor 102M.sub.z .sup.+. It will
further be noted that relative movement between the opaque pin and
light beam axes toward or away from each other may be effected by
either relative translational movement along one manipulator axis
or by relative rotational movement about the center of the sensor
in the plane extending transversely to the light beam axis, whereby
both force and torque vector sensing about the X, Y and Z axes is
possible, as will now be described.
The translational and rotational movements about the three
orthogonal manipulator axes are independently sensed by use of
pairs of properly located light sensors at diametrically opposite
sensor units. Reference is made to FIG. 3 wherein the sensors
102X.sup.+ and 102X.sup.- at the diagonally opposite units 25-3 and
25-1, respectively, along the Y axis are shown for sensing light
along light beam axes extending parallel with the Z axis. The
sensors are located at opposite sides of the Y-Z plane, that is,
the plane determined by the intersecting Y-Z axes. In the drawings
the sensors 102X.sup.- and 102X.sup.+ are shown located to the side
of the Y-Z plane in the positive and negative X axis directions,
respectively. With no X direction (i.e., sweep) force on the
manipulator, the outputs from the photocells 102X.sup.+ and
102X.sup.- are equal. A sweep force, however, will produce a
differential change in the photocell outputs. For example, a force
in the positive X direction will result in translational movement
along the X axis of the pins 84 within the housings 88, whereupon
the light reaching the photocell 102X.sup.+ increases whereas the
light reaching th photocell 102X.sup.- decreases. Conversely, a
sweep force in the opposite direction will result in a lower output
from the photocell 102X.sup.+ and a higher output from the
photocell 102X.sup.-.
The outputs from the pair of photocells 102X.sup.+ and 102X.sup.-
are connected to or included in a differential circuit having no
output when the photocell outputs are equal and having an output of
one or the other polarity dependent upon which photocell output is
the largest. Where the photocells 102X.sup.+ and 102X.sup.-
comprise phototransistors, a simple circuit such as that shown in
FIG. 7 may be employed. There, the phototransistor emitter and
collector electrodes are shown connected in series circuit between
positive and negative 15 volt supplies. With equal light
impingement on the phototransistors, equal currents flow
therethrough, whereby the potential at the output terminal 106 is
zero. If more light strikes one phototransistor than the other, a
positive or negative output voltage is produced, depending upon
which phototransistor is most conductive, the magnitude of which
output depends upon the light difference at the
phototransistors.
It will be seen that lift and reach forces on the manipulator
produce no change in the sweep sensing photocell 102X.sup.+ and
102X.sup.- outputs since, as noted above, such forces result in
relative movement of the opaque pins and associated light beam axes
having no component in the X direction to change the distance
between the light beam axes and pins. Similarly, it will be seen
that tilt and turn torques produce no substantial changes in the
photocell 102X.sup.+ and 102X.sup.- outputs. A twist force moment
(i.e., torque about the Z axis) will change the photocell
102X.sup.+ and 102X.sup.- outputs. Note, however, that since the
photocells 102X.sup.+ and 102X.sup.- are located at opposite sides
of the Y-Z plane, the photocell outputs change in the same
direction the same amount. For example, with a positive twist more
light is received by both photocells 102X.sup.+ and 102X.sup.-,
whereby the outputs therefrom increase. However, since the
photocells are connected in an electrical difference circuit
arrangement, as shown in FIG. 7, there is no resultant output
change at the output terminal 106 with equal changes in current
flow through the phototransistors. Consequently, sweep force
sensing by the photocells 102X.sup.+ and 102X.sup.- also is
substantially immune to torque about the Z axis.
The lift sensing photocells 102Y.sup.+ and 102Y.sup.- at sensing
units 25-2 and 25-4 are electrically connected together in a
difference circuit, such as the circuit for the sweep sensing
photocells shown in FIG. 7, the output of which circuit provides an
indication of the direction and magnitude of the lift force along
the Y axis. The photocell arrangement is similar to that of the
sweep sensing photocells at the orthogonally located sensing units
25-1 and 25-4 and requires no additional description.
The reach sensing photocells 102Z.sup.+ and 102Z.sup.- for force
sensing along the Z axis may be located at either diagonally
opposite sensing units 25-1 and 25-3 or units 25-2 and 25-4 and, as
shown in FIG. 3, are located at the units 25-1 and 25-3. The
parallel light beam axes for the photocells 102Z.sup.+ and
102Z.sup.- extend parallel to the X-Y plane at opposite sides
thereof. With a positive reach force, it will be seen that the pins
84 move rearwardly with respect to the housings 88, whereby the
photocell 102Z.sup.+ at the forward side of the X-Y plane receives
more light and the photocell 102Z.sup.- to the rear of the X-Y
plane receives less light. Again, the photocell outputs are
connected in a difference circuit (such as shown in FIG. 7) having
an output magnitude related to the reach force and polarity related
to the direction thereof. Also, forces along other axes and torques
about the X-Y and X axes either have no effect on the photocell
outputs or else produce the same change in both photocell outputs,
which changes cancel out in the output from the difference circuit
in which the photocell outputs are included.
Torque sensing about the X, Y and Z axes for measurement of the
magnitude and direction of tilt, turn and twist, respectively, now
will be described. The tilt sensing photocells 102M.sub.x .sup.+
and 102M.sub.x.sup.- are located at the diametrically opposite
sensing units 25-1 and 25-3, with the light beam axes associated
therewith extending parallel with the X axis. Both photocells are
located at the same side of the X-Y plane and, for purposes of
illustration, are shown forwardly thereof in the negative Z
direction. It will be apparent, then, that upon application of a
tilt torque, light at one photocell is increased while that at the
other is decreased. The photocell outputs are included in a
difference circuit, such as that shown in FIG. 7, the output from
which circuit has a magnitude dependent upon the amount of tilt
torque and a polarity dependent upon the direction thereof. The
only other movement whic produces a change in the photocell
102M.sub.x.sup.+ and 102M.sub.x .sup.- outputs is produced by a
reach force. It will be noted that positive and negative reach
forces result in increased and decreased outputs, respectively,
from both photocells, which cancel in the output from the
difference circuit.
Torque about the Y axis is measured by use of the photocells
102M.sub.y.sup.+ and 102M.sub.y.sup.- having outputs connected in a
difference circuit arrangement, which photocell and circuit
arrangement are similar to those of the X axis torque measurement
means described above and need not be described in any further
detail.
It will be readily apparent that twist may be measured by
photocells located at either pair of diagonally opposite sensing
units. In the drawings the photocells 102M.sub.z .sup.+ and
102M.sub.z.sup.- for twist measurement are located at the sensing
units 25-1 and 25-3 at the ends of light passages which extend
parallel with the Z axis and which are located at one side of the
Z-Y plane. As with all of the other pairs of photocells, the
photocell outputs are connected in a difference circuit, an
exemplary circuit arrangement being shown in FIG. 7.
Sweep and lift forces which result in translational movement of the
pins relative to their associated sensor housings load the coupling
means 26 in shear. The amount of movement for any given force will,
of course, depend upon the shear stress-strain characteristics of
the coupling means. A reach force subjects the coupling means to
either a tensile or compressive stress, depending upon direction,
and the amount of movement depends upon the tensile and compressive
stress-strain characteristics. Torque loading about any axis
subjects the coupling means to a combination of tensile and
compressive forces. Since the tensile and compressive stress-strain
characteristics of a material generally are quite different, it
will be apparent that a torque about an axis will result both in a
rotational movement and a small translational movement. The
accompanying translational movement, however, is not sufficient to
grossly adversely effect the outputs from the photocells, including
other photocells not utilized in the particular torque measurement,
and may be compensated for in the equipment using the sensor.
The coupling means 26 may be selected for the desired properties
and stress-strain characteristics for operation of the manipulator
within any desired range of force couples. Elastomeric material,
such as natural or synthetic rubber, plastic or the like, may be
used for the coupling means 26. Other suitable coupling means
include resilient beams, coil or leaf springs, or the like, having
suitable properties in shear, compression and tension for the
intended application. To further alter or extend the operating
range, composite coupling means 26 made, for example, of sections
or layers of different material may be employed.
The sensing method and means are not limited to use with the light
beam sensors described above. Other sensing units, including other
photocell-type sensors, potentiometer-type sensors and the like,
may be used at a radially spaced distance from the resilient
coupling for sensing the two perpendicular components of movement
mutually perpendicular to the radius therethrough independently of
radial motion thereat. Reference is made to FIG. 8 wherein a
supporting member 10' is shown connected through resilient coupling
means 26 to a supported member 18'. Force and torque sensing units
110-1, 110-3 and 110-4 (together with a fourth sensing unit, not
shown) are orthogonally located a radial spaced distance from the
longitudinal Z axis of the resiliently coupled members 10' and 18'
in a transverse plane extending through said coupling means 26.
Here, the sensing units each include two potentiometer-type sensors
designated 112-1 and 112-2, one for sensing movement parallel to
the Z axis and the other for sensing movement in a direction
mutually orthogonal thereto and to the radius therethrough. Each
sensor includes a first element comprising a rectangular shaped
plate of resistive material 114 and a second element comprising
contact 116 relatively movable over the surface of the resistive
plate in substantially point contact therewith. The resistive
elements 114 are attached to spaced longitudinally extending arms
82' on the supporting member 10' through insulating blocks 118, and
the cooperating contacts 116 are carried in blocks 120 of
insulating material attached to the supported member 18'. The
contacts, which are radially movable within the apertures in the
mounting blocks 120, are resiliently biased radially outwardly by
springs 122 at the base of the apertures, and output leads 124 are
attached to the contacts through said springs.
As also seen in FIG. 9, electrodes 126 are provided along a pair of
opposite edges of the resistive elements 114, which electrodes are
connected to equal magnitude but opposite polarity potentials V+
and V-. As viewed in FIG. 9, the electrodes 126 for the sensor
112-2 which are parallel to the Z axis are at right angles to the
electrodes for the sensor 112-1 which are parallel to the X axis.
With the contacts 116 at the center of the resistive elements, no
output voltage is obtained therefrom. Movement from the center
toward the V+ electrode will result in a positive output, and
conversely, movement from the center toward the V- electrode will
result in a negative output. It will be seen, then, that each
sensor is responsive to relative movement along one axis and is
insensitive to movement along the other axes. The pair of sensors
112-1 and 112-2 at any given sensing unit thereby provide outputs
indicative of movement from the neutral position along two
orthogonal axes mutually orthogonal to a third axis extending
radially through the sensing units.
Outputs from sensors at diametrically opposite sensing units are
connected to suitable difference circuitry to obtain the desired
force and torque output signals. In FIG. 10, to which reference now
is made, the outputs from sensors 112-1 at diametrically opposite
sensing units 110-1 and 110-3 are shown connected directly to one
differential amplifier 130 and are shown connected through an
inverter amplifier 132 to another differential amplifier 134. The
outputs from the amplifiers 130 and 134 are, therefore,
proportional to torque about the X axis and force along the Z axis,
respectively. Other pairs of sensor outputs are similarly connected
together in arrangements which will be obvious, in view of the
above description, to obtain other force and torque components, as
desired.
A force and torque sensing means employing sensing units of another
modified form is shown in FIGS. 11 and 12, to which FIGS. reference
now is made. As with the arrangement of FIG. 8, the supporting and
supported members 10' and 18' are coupled together through
resilient coupling means 26 to allow for relative movement
therebetween upon transmission of forces or torques therethrough.
Again, three of the four quadrature spaced sensing units designated
140-1, 140-3 and 140-4 are shown. Each sensing unit includes a pair
of light sources 142, such as light emitting diodes, attached to
one of the members 10' and 18' for production of radially directed
light beams. In the illustrated arrangement, the sources are
carried in blocks 144 attached to the member 18' and are positioned
to direct light beams radially outwardly through masks 146 having
square apertures 148 formed therein. The square cross sectional
shaped beams from the apertures impinge upon split photocells 150
having two adjacent light responsive elements at the face thereof.
Outputs from the two photocell elements are obtained from output
leads designated O.sub.1 and O.sub.2. At adjacent photocells 150 of
a sensing unit, the lines designated 152 between adjacent photocell
elements are perpendicular, as seen in FIG. 12, whereby movement in
two orthogonal directions mutually orthogonal to the line extending
radially through the sensing unit is detected. Photocell outputs
from diametrically opposite sensors are connected together in
difference circuits in the manner described above for the FIGS. 1-7
arrangement to obtain signals representative of the force and
torque components transmitted by the coupling means 26. It will
here be noted that outputs from commercial four-quadrant photocells
can be combined in sum and difference amplifiers to obtain the same
outputs obtained from pairs of two half photocells shown.
The invention having been described in detail in accordance with
the requirements of the Patent Statutes, various other changes and
modifications will suggest themselves to those skilled in this art.
For example, to prevent ambient light errors the wrist sensor
employing photocells may be enclosed in an opaque covering or
housing (not shown). Also, devices with only one pair of sensing
units, such as units 25-1 and 25-3 or units 25-2 and 25-4, may be
employed without the other pair for force and torque sensing of a
limited nature. Three sensing units spaced around the wrist (as
120.degree. equal spacing) also can be used to sense all three
forces and three torques. Here, either by proper placement of
photoemitting and photosensitive cells using difference circuits as
in FIG. 7 or by using only three pairs of light beams and
differential amplifiers to combine the outputs, all three forces
and three torques can be separately obtained. It is intended that
the above and other such changes and modifications which fall
within the spirit and scope of the invention will be covered by the
appended claims.
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